In the motor and building industries, it is common practice to extrude sealing sections either from a black thermosetting polymeric material which incorporates one or more fillers to reduce the cost of the extrusion or from a more expensive thermoplastics material. However, in each case, there is often a requirement for the extrusion to have its characteristics changed. For example, in order to stiffen up the polymeric material of a U-sectioned edge trim or door seal, a metallic carrier is incorporated within the extrusion. Alternatively (or additionally) a second polymeric material can be co-extruded with the first polymeric material. This is relatively easy with expensive thermoplastics polymers but not with thermosetting polymers. Hence, there is a requirement for rubber technologists to produce special rubbers which are compatible with and therefore competitive with the harder more expensive thermoplastics materials. For example, there is a requirement in both the motor and building industries for rubber extrusions to be provided which colour match motor car paintwork and/or upholstery in the one case and which colour match window frames and the like in the other, or which have a special decorative surface, or which have surface characteristics different from those of the main body of the extrusion.
It is also known to stiffen or reinforce internally thermosetting elastomer extrusions by using metal carriers. These are extremely satisfactory, but the metallic carrier is heavy and can rust, and is relatively expensive to manufacture.
There is therefore an ongoing requirement for providing a more satisfactory, less expensive product.
In GB-A-2109042 a rubber extrusion is disclosed wherein a coating of low friction polymer such as PTFE is applied to the surface of the extruded section by means of adhesive or spraying to reduce the frictional resistance of the extrusion. With many surface coatings, which are normally very thin, it is difficult and sometimes impossible to maintain a quality check on the extrusion and it is almost impossible to measure with instruments whether the coating is present or not. Furthermore, whether the surface layer be applied by means of spraying or adhesive, it is extremely difficult to obtain a satisfactory bond between the rubber and the surface coating, and the sprayed on coating is liable to cracking and crazing in use, whereas the adhered layer is liable to peeling off.
It is also known from GB-A-1545511 to co-extrude two different rubber materials so that the outer surface of the extrusion is different from the main body of the extrusion. For example, the main body of the extrusion may be formed of a relatively inexpensive rubber polymer and the surface of a different rubber polymer having desired characteristics. Unfortunately, however, such extrusions are difficult to produce and when the surface polymer is to be of a different colour from the main body of the extrusion, it is almost impossible to maintain colour quality and to match the colour with another colour because of the tendency for co-extruded rubber polymers to run together and merge. In any event, it is extremely difficult to clean out the extrusion apparatus satisfactorily when a change of colour is required and to co-extrude a particular coloured rubber polymer onto a basically black thermosetting polymer base.
In U.S. Pat. No. 4,513,044, a coloured rubber door seal is disclosed comprising a sealing portion of sponge rubber and a U-shaped trim or edge gripping portion of solid rubber with a metal carrier insert, there being a coloured solid rubber layer overlying the trim portion and a part of the sealing portion. The problems associated with GB-A-1545511 are also associated with this product.
It is also known from EP-A-0200618 and EP-A-0124955 to extrude thermosetting polymeric materials in the form of window channels or sealing strips and to incorporate into the thermosetting elastomer material a second polymeric material of low coefficient of friction which migrates to the surface of the extrusion to reduce its surface coefficient of friction. Such products, however, suffer from the disadvantage that they are principally formed of relatively expensive thermoplastics material.
In U.S. Pat. No. 4,538,380 a weatherseal is disclosed comprising a semi-rigid base member of polypropylene, a tubular sealing member of thermoplastic elastomer and a thin film of polypropylene, or a blend of polypropylene and thermoplastic elastomer, capping all or part of the tubular sealing member. The product is formed as a single extrusion, and the film provides a low friction contact surface to the thermoplastic elastomer sealing member which is resilient and compliant over a wide range of temperatures. Again, the extrusion is formed of expensive thermoplastic materials.
U.S. Pat. No. 4,676,856 discloses an extruded door seal which incorporates a thermoplastics polymeric carrier in place of the traditional metal carrier, around which a thermosetting polymer (rubber) is extruded. After extrusion the product is heated to cure the rubber and is then cooled so that the carrier becomes brittle so that it can be fractured along predetermined fracture lines to impart flexibility into the product, whereupon the product is heated in such a way that the carrier becomes soft again so that it can be formed into its required U-shape. Although the door seal disclosed in this specification is primarily formed of rubber, it is expensive to manufacture due to the several stages in the manufacturing process.
In EP-A-0209453, a method of making a composite extrusion is disclosed which comprises feeding into an extrusion die a thermoplastics material and a thermosetting material which have different extrusion temperatures, whereupon the resultant profile is cooled to below the softening point of the thermoplastics material, whereupon the thermosetting material is vulcanised.
In U.S. Pat. No. 4,537,825 and GB-A-1423541, there are disclosures of bonding thermosetting and thermoplastics materials together, in which a vulcanised blended thermosetting material has a thermoplastics elastomeric blend fused therewith. Because both polymers are blends, it is believed that a chemical bond occurs between the two polymers. The blended polymers are expensive and time consuming to produce.
In JP-A-49130470, there is a disclosure of coating a rubber tube with a thermoplastic blended co-polymer. The methods of achieving a satisfactory bond using extrusion techniques are not detailed.
It is also known to manufacture sealing strips with a semi-rigid base member formed for example of impregnated paper by means of which the strip is secured for example to a window frame, there being a flexible polyurethane foam bead projecting centrally from the base member with the whole being encapsulated in a sheath of polyethylene film by a continuous moulding process. This product is marketed under our Registered Trade Mark Q-lon.